Process for preparing rubberlike materials



Patented Oct. 22, 1946 PROCESS FOR PREPARING RUBBERLIKE- MATERIALS Byron M. Vanderbilt, Cranford, and Ralph'F. Plowe, Elizabeth, N. J assignor's, -by mesne assignments, to Jasco, Incorporated, a corporation of Louisiana No Drawing. 7 Application November'30, 1940,

Serial No. 368,106 i i 1 Claim. 1

This invention relates to the polymerization of olefinic substances into plastic, elastic substances; relates particularly to the polymerization of butadiene containing mixtures in emulsion form at moderately elevated temperatures; and relates especially to methods for speeding up the polymerization reaction and improving the character of the polymer obtained by the emulsion poly- 'merization of diolefin containing mixtures.

It has been found that when butadiene and similar substances are emulsified in water, either singly or in admixture with certain other unsaturated substances, at ordinary or elevated temperatures, and maintained in emulsion form for a prolonged period of time, a polymerization reaction occurs to produce materials having many of the properties of natural rubber, but as usually carried out, the products are of inferiorquality if the reaction mixture is heated to a sufficient temperature to get relatively complete reaction Within a few 'hours and if the reaction is carried out at a sufiiciently low temperature in order to get a product of high quality, the reaction time becomes a matter of even days or weeks and the process is economically unfeasible.

The present invention provides a combination of steps by which the polymerization reaction is greatly speeded up, and at the increased reaction speed a polymerizate is obtained which has a high tensile strength, and satisfactory plastic and elastic properties.

According to the present invention,1the procedure consists in thepreparation of an emulsion of butadiene, with, or withoutauxiliary olefinic polymerizable substances such as acrylonitrile and the like, in water, with an emulsifying agent, preferably of the soap type, and a catalyst of'jthe peroxide type presentin optimum concentration;

in which the hydrogen ion concentration or pH According to'the invention, thepolymerizable materials; are preferably selected from such substances as butadiene or mixtures of butadiene with such. substances as acrylonitrile, styrene,

; vinyl naphthalene, unsaturated esters unsaturated ketones, and similar polymerizable substances. These materials form the polymerizanble reactive component of the polymerization mixture, and may be used as butadicne alone, or

I as buta'diene-in admixture with one or more of able emulsifying materials.

the other substances, in which mixture the butadiene maybe present in theratio of from 30% to the 100% of totalreactants. The butadiene, or butadiene mixture, emulsified in water in the proportion of 100 parts of butadiene material or mixture with from 100'parts to 500 parts of water. The mixture preferably contains an emulsifying agent such as sodium oleate or sodium stearate or sodium palmitate or other soap, or other suit able emulsifying agents such as the salts of sulfated long carbon chain amides and alcohols, alkylated naphthalene sulfonates, and other suit- The emulsifier may be present in the proportion of from 0.5 part to parts per 100 parts of olefim'c material. There is preferably also added a, substantial amount of a peroxide catalyst such as hydrogen peroxide, benzoyl peroxide, ammonium persulfate, or other soluble organic or inorganicperoxide material which is desirably present in the proportion of from 0.05 part to 3 parts per 100 parts of olefinic mixture. The pH of the mixture is then adjusted by the addition ofsmall quantities of certain acidic'or basic materials'until it is set at a value lying between 8 and 8.8. This mixture is conveniently charged into a metallic vessel with means for efficient mixing of the, mixture in order to maintain the olefinic material in an emulsion form and to facilitate removal of the a heat of reaction. The temperature may be held within the range of 20 to 30 C. for from 1 to 8 hours; withinthe range of 25 to 4030. for a further period of from 2 to 10 hours, andand a temperature ranging from 30-to50 C. for a further i or oth.

period of from 4 to 12 hours. At the end of this interval the reaction vessel may be opened, any unreacted ,butadiene ,volatilized out, and the emulsion-broken by the addition of suitable preacid or water-soluble salts cipitants such as an an object of the invention is to speed up the polymerization reaction of olefinic materials and obtain preferred characteristics in the polymer or interpolymer by the addition of the olefinic material to water containing an emulsifying agentwhile stirring; the addition of a suitable catalyst and conduct of the polymerization reaction under conditions of accurately adjusted hydrogen ion concentration and. the application of a, greater? rising temperature schedule. Other objects and details of the invention will be apparent from the following description.

Example .1

A mixture was prepared consisting of 420 parts of water containing 2.5% of sodium oleate by weight andpfifi aparts -of acrylonitrile with good 5 mixing. This mixture was transferred to, a metallic pressure vessel which was properly sealed,

and 160 parts by weight of butadiene were forced e in by the application of nitrogenunder pressure.

Thereafter parts by weight of 27%hydr g n;10.

olefin materials in the emulsion condition, and

the heating and agitation were; continued .ior ,a period of 3 hours. At the end of this time the unreacted butadiene was allowed to volatilize out I of the mixture, the residual emulsion -was- -removed from the bomb and the polymerizate precipitatedby the applicationthereto of 2.5 volumes of saturated sodium .chloridesolution. 1 imparts byweight oi -polymer were iobtained, this being 51% of the original reactants added to, the mixture, and being a 51%. yield ofthe theoretical maximum yield.

This material was washd driedand compounded on a rubber mill according to the followingformula:

- "This -material= ;was yulcarrizedin. a mold at a; temperature of 145 Cwf-ora time intervalof 45 -minutes and after being removed from the v mold and cooled showed atensile strength of 31.00 45 pounded according to the formula shown in Example l and then vulcanized, showed a tensile strength of 3100 lbs/sq. in. and an elongation at break of 450%.

Example 5 An emulsion was prepared as in Example 1, and, without heating, it was stirred vigorously to maintain the emulsion for a time interval of =6, /z-hours during which the temperature was maintained within the range of from 15 C. to 18 40. At the close of this time interval, the re- .actionvessel-was opened and the butadiene was allowed tovolatilize out and was recovered. No

solid polymer was found in the mixture, and subustantially.all of the butadiene and acrylonitrile :gwere; recovered unchanged.

\ Partsu 'Polymer 10 a Wood rosin 4' 'Coal tar 4 Sulfur 1.5

' Stearic --acid L 11535 Ozokerite-wax 1.5 Zinc oxide 5 Carbon black '45 Altax (benzo-mercapto thiazole) 1.25 Diphenylguanidine' 0.25-40 as shown in Example 1,' and the emulsion wasm I heated at a temperature of C.-'for 4 hours (one hour longer thanExample 1). The resulting polymer amounted to 60% of the original reactants, which upon curing according .to: the

- above formula. yieldedlmaterialrhaving a tensile 'tion at break.

"Example-:3

Another run .usinga similar mixture polymer-, ized at 60 C. fora time interval of 5 hoursgave a yield amounting to 81% of the reactants, and

the polymer when compounded according to the above formula and cured had a tensile strength of 2400 lbs. /s q.' in. andanelongation at break IA similar olefinic -mixturewas prepared as in mer was 58 .ofdthe ,theoretical,.maximurn; and

Q surevessel by th application of nitrogen pressure to thejolefinic mixture in a suitable, conthe polymer upon being precipitated and com-' .a time interval of 2 hours. I perature was raised .to 30 C. for a further period merizationtime of 16, hours. time interval, the pressure vessel was opened and the unreacted butadiene allowed to distill' off. 1 The residual latex was then withdrawn to a larger container andthe polymerw'as-precipitatedby This example shows the extremely slow reaction rate, or lack of polymerization, at room temperature.

' Example 6 An .emulsion -was prepared asrinrExample 1 and heated according to a temperature schedule inwhichthe temperature was held at 25, C.

for a time interval of. 4. hours; 30?, CLfora further time interval of: 8,hours;, andj40 C. fora still further timeinterval of 9;hours. Otherwise, the composition of the reaction. mixture and the experimental conditions-were exactly as those for the. above examples. The polymer was separated as in Example 1 and was found to -be of the theoretical maximum. It wasthereafter compounded according to the formula shownvinrExample 1 and vulcanized in ,the 'samegmanner. After vulcanization it had atensile .strength of 4500 lbs/sq. in. and an elongation atybreak; of

' The above examples shown the marked advantage of atime and temperature schedule in which the temperature starts at a relatively low value and is raised gradually during the polymerization reaction to yieldv a product of high quality in'a relatively short time.

Example 7 This ,experimentwas conductedin a pressure .vessel or bomb equipped with a turbine mixer, by

which sufficiently rapid agitation could be obtained to bring the olefinic materials into a-good emulsion. 2600 parts by weight ofwater were v placed in the reactor, together with65 parts by weight of a water, soluble soap, specifically sodium oleate and 16 parts ,by weight of 27% (hydrogenperoxide. The pressure vessel was then closed and the stirrer started in-yigorous rotation. Thereafter a'mixture consisting (of 325 parts by. weight of acrylonitrile and 975pparts by weight ,of butadiene was forced into the prestainer. 'jThepressure vessel was'fillednearly full,

.to minimize the amount of vaporized butadiene,

and when the emulsion was well formed; the ternperature was raised to 25 C. and held'theregfor Thereafter the temof.6 hours and further raised to 40 C. for-a further period of 3 hours, making a totalpoly- At the; end of this the addition of approximately I vo1ume-0f--salt found that the hydrogen ion value is exceedingly. I critical for the obtaining of a rapid reaction and a high grade polymer. According to the present invention, it is found that the polymerization of diolefins such as butadiene or the interpolymerization of diolefinssuch as butadiene with other unsaturates such as acrylonitrile, styrene, Vinyl naphthalene and the like to form vulcanizable rubberlike materials occurs at an extremely slow rate, or does not occur at all if the pH value of the polymerization emulsion lies.

between about 6.5 and 7.5,in the presence of polymerization catalysts. If polymerization is obtained at all in this pH range, the rate of reaction is slow and the polymers obtained are inferior in nature. At elevated temperatures, such emulsions containing butadiene alone, or

mixtures of butadiene with acrylonitrile, styrene,

vinyl naphthalene and similar substances polymerize either extremely slowly or not at all at pH values between about 7.0 to 7.7. In the pH range of from 7.7 to 8.1 polymerization occurs at fairly rapid rate but the emulsions or latices formed are unstable and tend to precipitate in the reactor. The preferable pH range lies between the values of about 8.1 to about 8.8. With-,

in this range polymerization occurs rapidly to form elastic polymers in good yield of high tensile strength and high elongation. The best results are obtained at pH value of approximately 8.4. As the alkalinity is raised about about 8.8, r

the reaction becomes progressively slower with increasing hydroxyl concentration. The emulsions formed are stable but the products obtained are of lower quality as compared to those obtained atthe preferred hydrogen ion value.

Example 8 An emulsion'of butadiene and acrylonitrile was prepared as in Example 7 and the pH value was raised to 9.6 by the addition of small quantities of sodium hydroxide solution. The emulsion was then heated in the pressure vessel to'a temperature of 25 C. for a time interval of 4 hours, then to 30 C. for a further time interval of 8 hours,

then to 40 C. for a still further time interval of 8 hours and then to 50 C. for an additional time interval of 1 hour. The reaction was 78% complete after 21 hours and the polymer after compounding and vulcanizing had a tensile strength of 4300 lbs/sq. in.

Example 9 An emulsion was prepared as in Example 7 and the pH value was adjusted to 8.45. Thereafter the mixture was heated according to the time schedule set out in Example 8. At the end of the 21 hours'reaction time, the polymer was separated and the reaction found to bej93% complete." The polymer was washed, compounded according to the formula given'in Example 1, vul- 6 canized in the manner above shown and was then found to have a tensile strength of 4420 lbs/sq. in. and an elongation of approximately 550% at break. r

Exa ple 10 A mixture of the following composition was prepared in a pressure vessel of the turbine mixer type: V

Parts by weight Water 1 1 850 Igepon T (sulfated long carbon chain amide) r A l r '10 Acrylonitrile i 113 Butadiene .320 Hydrogen peroxide (27%) 20 mixture was heated at a temperature of 50 C. for a time interval. of.2 2 hours. At the close'of that time substantially all .of the butadiene and acrylonitrile were recovered unchanged from the mixture and no polymer was found to have been formed showingthat no polymerization reaction occurred. It may be noted that the Igepon T is neutral and. the above mixture was neutral, having a hydrogen ion value of approximateIylO' Example 11 1 A similar mixture to that of Example 10 was prepared and 2 parts by weight of normal sodium hydroxide solution was .added. This mixture Was heated at a temperature of 50 C. for 22 hours. At the close of this interval, of the reactants were found to have polymerized to a high-grade, rubber-like polymer.

Example 12 A similar mixture to that of Example 10 was prepared except that 2 parts by weight of normal acetic acid solution Was added to the mixture. The emulsion was then heated to a temperature of 50 C. for 22 hours. At the end of this time the reaction was complete, but a relatively large amount of the productwas found as a dense coherent precipitate in the reaction vessel. l l r Example 13 A mixture was prepared in a pressure vessel equipped with a turbine stirrer as in Example 10, consisting of the following materials:

l i Parts by weight Water 395 Dodecyl amine 7.4 0.94 normal acetic acid; 30 Acrylonitrile 56. 3 Butadiene 160 Ammonium persulf'ate 0. 2

This mixture had an initial pH value of 7.0. It was heated according to the schedule of Example 8 with eflicient stirringwto maintain the emulsion. At the end of the 21 hours, the butadiene was distilled out and parts of the orig- 1 inal parts were recovered. Only a little dark brown oil was formed as a polymerizate.

. Example 14 A mixture similar to' that of Example 13 was prepared butwith 36 parts by weight of the acetic acid solution; thereby adjusting the pH to avalue of 6.2. A 62% yield of good polymer was obtained after heating identically as was Example 13, which after washing, compounding, and vulcanizing as in Example 1, was found tohavea tensile strength of 3900'pounds per sq. in.

taining 8 par-ts of sodium lauryl sulfate waswell agitated While adding-.5Qparts of styrene. Four parts of trisodium phosphate was then added and the emulsion was found to have a pl-l of lll.

'" 'The mixture was placed in a pressure vessel and i catalyst. content :increaseslthe reaction rate and thisais particularly so with-substantiallyallother .olefinic polymerization'reactions.

Example )1 6 3A: mixture was preparedin-the pressure-reactor i asrin Example 13 according-to the following formula:

then 150 parts of butadiene containing 1 partlof Partsby'weight :benzoyl peroxide was added under pressure while 10 ater 380 -mixingr -The reactionmixturewas then heated odecyl amine 7.4 to 50 C. fora period of 17-h0urs. It Was-found 0-943 ormal acetic acid 40.8 hthat 35% of thetotal weight of -the-styrene and fi y -ile a. 56.3 butadiene had been converted, to a rubber-like Onl11m persulfate 0.8 solid. 15 Butadiene 160 This preparation Was 'repeated:-and modified inthatsodium bicarbonate was ,used as buifer to givean initial pH of 8.5. Afterthe 17 .hour reac- This mixture .was heated, for; a,time interval 0f121. hours. according to the temperature schedtion period at 50 .C. .-a. :concen-tratedlatex was formed. which, i on coagulation .with. isopropyl. al-

. .cohol, gave. 152 parts of polymer: of high tensile strength, a '76 yield.

It. has been. found that not .onlyare. the .hy-

. drogen,v ion and temperature schedules of very great importance, butit. has alsobeenjoundthat sulfate or .the-like should be'present in an amount of 0. 05 to 0.3% of .the aqueous-phase. Athigher values than. 0.3%- the resulting polymer is: of lower tensile. strength and has inferior-plastic properties and the rate of reaction ismarkedly decreased. On the other hand, if the initial concentration of the catalyst isless than about 0.05% in the aqueous phase, the reaction proceeds less rapidly andrwhen the catalyst concentration is aslow as 0.01% of ,the water-phase; the reaction rate is approximately that obtained when no catalyst is present.

'I'hefollowing table shows the, effect of "change in concentration of hydrogen peroxide catalyst in the water phase when copolymerizing a mixture of of acrylonitrile and 75% butadi'ene in emulsion at a pH of 8.4:

' It will be observedvfrom this table that'gtheopti- :mum'concentration of catalyst lies in the, :range ..o f;about 0.05%to0.1%. I y

It may be. noted that -the:;.cata1yst proportion in this mixture, showsan optimum valueat which a. maximum rate of polymerization occurs. This phenomenon is entirelycontrary to most polymerization reactions. {In the presentrinstance, as the catalyst;concentration is-increased from 2 or 3 hundredths of -l,%.up to approximately 0.075%,

the; reaction rate increases Wi-thincrease incon- .scentration; when; how ever,--v the;catalyst concenrtr ation1isiincreaseduabove about 0.1%.thereac- .tion 1 rate decreases. .This-isin contrast atolmost catalytic processes; inwhich: an increase :in the A similar mixture to that in Example 16 was prepared with only 0.2 part by weight of ammonium persulfate. This mixture'wasstirred and allowed to react through the same time schedule as in Examples 8 and 16. At the end of the reaction period the unreacted butadiene wasfldistilled off, the polymer precipitated and found to consist of approximately 80% of the original reactants.

" This emulsion was'recovered from the reaction chamber as a latex of good color'which after precipitation, washing, compounding, and vulcanizing as in Example 1, was found to have a good tensile strength and satisfactoryelongation and plastic properties.

? The above examples utilize mainly mixtures of butadiene and acrylonitrile, but the same factors and values apply to mixtures containing only 'butadiene as the reactant and to mixtures con- Percent'converted .Samples'removed'after talining'both Pufmdiene styrenegvinyl methyl mom-the P 9 I ketone and similar unsaturates. Likewise, while waterphase only hydrogen peroxide-and ammonium persul- 20 h 21 22 hrs Tensile fate and benzoyl peroxide, are shown as catalysts,

V strength elongation 7 p thesame requirements: and similar molar values 4 apply for 'the'other peroxidecatalysts; such as .Pggem 77 81 itt? 500 odium perborate. 'Modifying agentssuch as or- 8-? g? 33 ganic= sulfur'v compounds may al'so be added in M 4:400 order .tmmodify the polymerization process in (1-038 gg g fg order to obtain more plastic products. Similarly, while a fewrepresentative temperatureschedules aregiveng'it'willbe appreciated bythose skilled in 'thezartithat diilerent unsaturates require different temperatures for polymerization and the "invention comprises the use of anytemperature schedule in which a progressively increasingtemperature is used at progressively latertimes inthe course of the polymerization reaction.

It should be understood that the materials employedin' the various examples cited above were of=-c0mmercial jgrade. By using diolefins and other cop'olymerizing materialsxof very high purity, the reaction periodimayb greatly decreased. Forfexample; when highly purified butadiene and acrylonitrile 'were ,:used .in the processes as described above; :the copolymerization reaction-was 175. 75;%r complete, after only 'l-hours and the: rubberlike material obtained was of excellent quality.

It should be appreciated that difierent diolefins, singly and with other olefinic materials capable f lw y e g in emulsion form, vary in their activity at a given temperature. Vinyl naphthalene is less reactive with butadiene than is styrene and a higher initial temperature is required. Also acrylonitrile is more reactive with butadiene than is styrene and mixtures of acrylonitrile and butadiene containing 40% acrylonitrile are more reactive than those containing 15% of the nitrile. Thus the optimum temperature range employed will vary with the reactants employed, but temperatures above about 60 C. and below about 25 C. are undesirable, regardless what olefinic reactants are employed.

Although we prefer to use our stepwise temperature control, We also may use a constant reaction temperature. When using a constant reaction temperature of about 40 C. at a pH of 8.4, a faster reaction and a superior polymerizate is obtained as compared to those obtained at a like temperature outside of the 8.1-8.8 pH range.

Thus, the invention consists of an emulsion polymerization reaction of olefinic materials to produce rubber-like polymers in which the emulsion is maintained by a suitable emulsifying agent, the polymerization reaction is promoted by a catalyst in concentration of 0.02 to 0.3% in the water phase, the pH value is maintained between about 8.1 and 8.8, a gradually rising temperature schedule for the polymerization time is used to produce a very high grade polymer having high tensile strength, high elongation, and other desirable physical characteristics and the polymerization process is accomplished in a relatively short time.

While there are above disclosed but a limited number of embodiments of the invention, it is possible to produce still other embodiments without departing from the inventive concept herein disclosed, and it is therefore desired that only such limitations be imposed upon the appended claim as are stated therein or required by the prior art.

The invention claimed is:

In an emulsion polymerization process for the polymerization of a mixture of butadiene and acrylonitrile in the ratio of about three parts by weight of butadiene for each part by weight of acrylonitrile, the steps in combination of mixing the mixture of butadiene and acrylonitrile with Water in the presence of an emulsifying agent comprising a water soluble soap and a peroxide polymerization catalyst, agitating the material to maintain the mixture in emulsion in the water, setting the temperature of the mixture at approximately C., holding the temperature at approximately 25 C. for a time interval of approximately four hours, then raising the temperature to approximately C. for a further time interval of approximately eight hours, then raising the temperature to approximately C. for a further time interval, maintaining the pH value of the material within the range between 8.1 and 8.8 during the entire polymerization reaction, cooling the material at the encl of the polymerization, and separating the polymer from unpolymerized olefinic material.

BYRON M. VANDERJBILT.

RALPH F. HOWE. 

